# MachineDiscovery/detect_CPUs.py
def detect_CPUs():
    """
    Detects the number of CPUs on a system. Cribbed from pp.
    """
    # Linux, Unix and MacOS:
    if hasattr(os, "sysconf"):
        if os.sysconf_names.has_key("SC_NPROCESSORS_ONLN"):
            # Linux & Unix:
            ncpus = os.sysconf("SC_NPROCESSORS_ONLN")
            if isinstance(ncpus, int) and ncpus > 0:
                return ncpus
        else: # OSX:
            return int(os.popen2("sysctl -n hw.ncpu")[1].read())
    # Windows:
    if os.environ.has_key("NUMBER_OF_PROCESSORS"):
            ncpus = int(os.environ["NUMBER_OF_PROCESSORS"]);
            if ncpus > 0:
                return ncpus
    return 1 # Default
    